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2000-01 The Bobtail Squid

Denise Neilson Tackett

The Bobtail Squid, Euprymna sp., is a sepiolid cephalopod, a soft-bodied invertebrate related to octopuses. Like other cephalopods, it has sucker-lined arms and a sharp beak for capturing prey. It moves about by squirting jets of water through its siphon. Specialized skin cells called chromatophores help to camouflage this sepiolid from predators and prey by allowing rapid color changes from white to rust to brilliant blues and greens. Like its relatives, it has a short life span—less than a year.
Bobtail Squid can breed at about two months old. Males have one or two arms specialized for transferring sperm to females and for displacing sperm previously deposited by another male. Clusters of eggs are attached to the substrate and are lightly coated with sand. Shortly after birth, this species captures luminescent bacteria from the water column for storage in its light organ. These symbiotic bacteria continue to to live and produce bioluminescence, which helps to disguise the sepiolid’s shape at night by breaking up its outline.
This diminutive cephalopod, which is more like a cuttlefish than a squid, is only 10 to 30 millimeters long. It lies buried beneath the sand during the day and emerges at night to feed on tiny crustaceans. When it reburies itself, it hunkers down in the sand and uses two arms to toss sand grains up over its back. Special glands secrete a mucous coating to which sand adheres, contributing to its camouflage. When confronted with a predator, the Bobtail Squid quickly sheds its mucous envelope and darts away before the predator realizes what has happened. Sepiolids are found in tropical and temperate waters of the Indo-Pacific region.